A heat exchanger of this type is known from European published patent specification EP 0 344 206A, which discloses a heat exchanger with an integrated filter, comprising:
a casing delimited by a cylindrical wall which is symmetrical about an axis; a first end wall; and a second end wall, PA1 a filter compartment disposed in an axial region of the casing and containing a tubular filter cartridge, PA1 a heat exchange compartment of annular configuration, disposed between the filter compartment and the cylindrical wall of the casing, PA1 heat exchanger means disposed in the heat exchange compartment so as to define therein a first chamber for flow of a first fluid and a second chamber for flow of a second fluid,
and in which the first chamber communicates firstly with a first inlet for the said first fluid, and secondly with the filter compartment, which is in communication with a first outlet for the first fluid, the said first inlet and first outlet being arranged on the first end wall of the casing, while the second flow chamber communicates with a second inlet and a second outlet for the said second fluid, the said second inlet and outlet being arranged on the said cylindrical wall of the casing. Such a heat exchanger will be referred to herein as a heat exchanger of the kind specified.
In the case where such a heat exchanger is used for cooling and filtering the lubricating oil of a heat engine, this oil constitutes the first fluid. The second fluid is then typically the engine coolant, usually comprising water to which anti-freeze has been added.
In the above known type of heat exchanger, the heat exchange means consist of a simple cylindrical separating wall which divides the heat exchange compartment so as to define within the latter the said first and second chambers. The first chamber is disposed between the cylindrical separating wall and the filter compartment, while the second chamber is defined between the cylindrical separating wall and the cylindrical outer wall of the casing.
In addition, the first chamber is separated from the filter compartment by a perforated wall which has a multiplicity of perforations distributed over its whole periphery and over its whole depth. These perforations are such that the first fluid, after having been cooled by heat exchange with the second fluid, passes through the perforations so as to reach the filter compartment, in which it is filtered by passing through the tubular filter cartridge. The first fluid passes radially through this tubular cartridge, and is collected in a central duct which is connected to the first fluid outlet arranged on the first end wall of the casing.
Such a heat exchanger, as described above, has various disadvantages. Firstly, it is found that some of the first fluid penetrating into the first chamber has a tendency to pass directly through the perforations of the perforated wall, which lie close to the first inlet of the casing, without having undergone heat exchange with the second fluid. Thus, in the case where the first fluid is lubricating oil which ought to be both cooled and filtered, there is always some part of this oil which is filtered without having previously been cooled.
Another disadvantage of the above known type of heat exchanger lies in the fact that the heat exchange means comprise a simple cylindrical wall which, consequently, offers a minimal heat exchange surface. As a result, the heat exchanger as described in the above mentioned European patent specification is very limited as to its heat exchange performance, and is unable to offer optimal cooling to the first fluid, especially when the latter is engine lubricating oil.